It’s almost as if Chris Johnson fits perfectly with this ragtag bunch of Celtics, so much so that it’s difficult to notice he’s been here just six weeks.

Johnson has cemented himself as part of the rotation, emerged as a sparkling 3-point shooter, and will be part of training camp next season as part of the contract he signed for the remainder of the season.

Johnson worked arduously during two 10-day contracts, and despite the Celtics’ reluctance to add salary, they locked up the swingman, rewarding him for adapting quickly to coach Brad Stevens’s offense.

In 17 games, Johnson is averaging 6.5 points and shooting 39.7 percent from 3-point territory.
He is 3 for his last 16 from the arc, as opposing defenses have scouted his outside shooting prowess and have forced him to put the ball on the floor. Such attention is flattering for a player who was an NBA afterthought a couple of months ago.

“I feel like I can do more than just shoot the ball,” Johnson said. “Coaches know what guys can do. I can do other things, provide energy, and do other stuff to help the team win. I’m just trying to get better. It’s a good thing [to be scouted] but you have to find other ways to do things.”

Johnson has gained the admiration of teammates with his energy and work ethic. Those players who have guaranteed contracts respect a player who came up through the Development League and was forced to make an impression on 10-day contracts.

The NBA is a difficult business. On Wednesday night, Hawks center Dexter Pittman was working up a sweat before the game against the Celtics, in the middle of his 10-day contract. On Thursday, he was released so the Hawks could sign former Bucknell big man Mike Muscala. For players such as Johnson, unpredictability is part of the challenge.

“It’s definitely a blessing to reach your dream of being here,” said Johnson, who was the most valuable player of the 2010 National Invitation Tournament for champion Dayton. “You have to make the most out of your opportunity. You never know how long you are going to play in this league or what happens. While I’m here, I’m making the most of it and going all out.”

Johnson received a taste of the highest level last season with an eight-game stint with the Memphis Grizzlies, but after his second 10-day contract expired, he headed back to the NBADL Rio Grande Valley Vipers. Johnson spent a month in Brooklyn Nets camp before being released in late October, and after another stint with the Vipers he got his opportunity with the Celtics.

“First of all, you have to have faith, and I have faith,” he said. “I just work hard and it all paid off. Last year it was kind of up and down, but this year it was a different mind-set for me, and I went into the D-League and had a different approach and I was going to give it all I can every time out there on the court and in practice, and I made the most of it.”

Johnson has blended in well with his new teammates, who treat him as a rookie, as they do with Phil Pressey and Kelly Olynyk. But they have regard for Johnson’s journey.

“I love it,” said
Brandon Bass, a second-round pick in 2005. “I’m always going to root for the underdog because that’s who I am. I had to work my way up in this league. I’m happy for him. It’s great to see him out there consistently playing, getting minutes, and actually helping us. There are players in the D-League and overseas with the talent to play in the NBA, but some have that determination and Chris is one of them.”

Sullinger improved

Jared Sullinger said Thursday he is feeling better and could return to practice on Friday. The second-year forward has missed the last three games because of a concussion suffered when he was flattened by an elbow from Chris Kaman in the Feb. 21 loss to the Lakers. Sullinger has to pass the NBA’s concussion protocol before being cleared to play. Stevens said Sullinger will miss Saturday’s game against the Pacers . . . Olynyk was wearing a boot on his left foot to protect a sprained toe suffered in last Saturday’s loss to the Kings. Olynyk played Monday in Utah, scoring 21 points, but underwent X-rays afterward, which were negative. “It’s sore. It hurts. No, I can’t tell you [how it happened],” he said. “I wish I knew. It happened in Sacramento game, it was really, really sore. Then I taped it and tried to play in Utah. I was just running on the outside of my foot.” . . . The Celtics are expected to sign guard Chris Babb to a 10-day contract, league sources told the Globe. He could be available Saturday against Indiana. Babb has been playing with the Maine Red Claws of the Development League, where the former Iowa State standout has averaged 11.9 points, 6.1 rebounds, and 3.1 assists in 32 appearances. Babb was with the Celtics during training camp and impressed them with his outside shooting during several exhibition games. The 6-foot-5-inch shooter’s addition will help with starting guard Avery Bradley sidelined with a sprained right ankle.